Why blender doesn't render my trees
you did something, which Blender does not support this way.
You cannot put a particle system as rendered object for another particle system.
If you change the rendered object to e.g. path here:

then Blender renders something - of course NOT what you want. But this answers your question.
Then you get this render output:

By the way: Why did you use hair as particle system? For trees the &quot;normal&quot; particles are good to go...